Hello. Right now the stand alone games can not be played in multiplayer. They don't contain the markers and steam client is required to play Multiplayer. This also means that you must own Game Guru right now to play multi player.
There is a feature on the community voting page that deals with this. There will be a module later down the line for this when that feature reaches the number 1 position.
That can be viewed here, and you can cast your vote also.
https://www.game-guru.com/feature-voteIntel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit
